LTE and LTE-A aim at addressing the increasing requirements for broad band services in high user density areas while maintaining good performance in extreme channel condition such as high mobility of high speed trains. Scale and speed of High-Speed Rail/Highway (HSR/HSH) are rising continually. The top operation speed of HSR even reaches 380 km/h.
Increasing of speed will result in decreasing communication quality of passengers. Effect of Doppler is obvious and Doppler shift produces a greater negative impact on quality of mobile communication traffic in HSR/HSH. Therefore, communication operators and equipment manufacturers are anxious to resolve related issues. Users have great potential requirements in the scenario. And mobile communication coverage has its specified characters in HSR/HSH comparing with that of other scenarios.                (1) Nowadays most of LTE and LTE-A Base Stations (BS) are deployed at high frequencies (e.g., 2.6 GHz) which results in higher Doppler shift than that of low frequencies (e.g., 700 MHz).        (2) Variety of Doppler shift is not frequency linearity. It depends on not only the speed of UE but also the angle between moving direction of UE and BS.        (3) UE goes through a cell in a very short time, which results in the frequentness of Doppler shift are changed quickly. That will increase frequency shift, Block Error Rate (BLER), etc.        
In radio access network, there are a lot of standards (2G/3G) consider the effect of Doppler, especially for LTE and LET-A (4G). LTE and LTE-A adopt OFDM requiring carries orthogonal. Restraining Inter-Cell Interference (ICI), estimating and compensating frequency shift are vital technologies. Therefore issues of Doppler shift are important for mobile communication system.
Standards [1] [2] [3] of 3GPP special describe propagation conditions of high speed train scenario. They show the simulation results of Doppler shift trajectory. However they just suppose the velocity is uniform and doesn't propose any methods to overcome Doppler shift.